Human immunodeficiency virus and hepatitis C infections induce distinct immunologic imprints in peripheral mononuclear cells

Coinfection with hepatitis C virus (HCV) is present in one-third of all human immunodeficiency virus (HIV)-infected individuals in the United States and is associated with rapid progression of liver fibrosis and poor response to pegylated interferon (IFN) and ribavirin. In this study we examined gene expression profiles in peripheral blood mononuclear cells (PBMCs) from different groups of individuals who are monoinfected or coinfected with HIV and HCV. Data showed that HIV and HCV viremia up-regulate genes associated with immune activation and immunoregulatory pathways. HCV viremia is also associated with abnormalities in all peripheral immune cells, suggesting a global effect of HCV on the immune system. Interferon-alpha-induced genes were expressed at a higher level in PBMCs from HIV-infected individuals. HCV and HIV infections leave distinct profiles or gene expression of immune activation in PBMCs. HIV viremia induces an immune activated state; by comparison, HCV infection induces immunoregulatory and proinflammatory pathways that may contribute to progression of liver fibrosis.

CONCLUSION

An aberrant type-I IFN response seen exclusively in HIV-infected individuals could be responsible for the poor therapeutic response experienced by HIV/HCV coinfected individuals receiving interferon-alpha-based current standard of care.

Isolation and quantitation of HIV in peripheral blood

Quantitation of replication-competent human immunodeficiency virus (HIV) in peripheral blood of infected individuals is critical for investigations of HIV pathogenesis and therapy. In this unit, the basic protocol determines the HIV titer in seropositive blood by measuring the tissue culture infectious dose (TCID) by an end-point dilution method. A second basic protocol utilizes the PHA-stimulated T cell blasts (activated T cells) in co-culture with PBMC as described in the first basic protocol for the short-term growth of HIV in vitro. An Alternate Protocol describes the accumulative method of determining 50% tissue culture infectious dose (TCID(50)) of HIV using the Reed-Muench equation when multiple replicates of a given sample are employed in the assay. A consequence of HIV infection is the depletion of CD4(+) target cells, evidenced by syncytia formation or single-cell death; two support protocols detail the evaluation of these cytopathic effects.

Gene Expression Profiles in Hepatitis C Virus (HCV) and HIV Coinfection: Class Prediction Analyses before Treatment Predict the Outcome of Anti‐HCV Therapy among HIV‐Coinfected Persons

Therapy for hepatitis C virus (HCV) infection in human immunodeficiency virus (HIV)-infected patients results in modest cure rates. Gene expression patterns in peripheral blood mononuclear cells from 29 patients coinfected with HIV and HCV were used to predict virological response to therapy for HCV infection. Prediction analysis using pretherapy samples identified 79 genes that correctly classified all 10 patients who did not respond to therapy, 8 of 10 patients with a response at the end of treatment, and 7 of 9 patients with sustained virological response (86% overall). Analysis of 17 posttreatment samples identified 105 genes that correctly classified all 9 patients with response at the end of treatment and 7 of 8 patients with sustained virological response (94% overall). Failure of anti-HCV therapy was associated with elevated expression of interferon-stimulated genes. Gene expression patterns may provide a tool to predict anti-HCV therapeutic response.

Expression of Chemokine and Inhibitory Receptors on Natural Killer Cells: Effect of Immune Activation and HIV Viremia

We examined the cell-surface expression of chemokine and natural killer (NK) cell inhibitory receptors (iNKRs) on NK cells from individuals with human immunodeficiency virus (HIV) infection, chronic hepatitis C infection, and Wegener's granulomatosis (WG), an inflammatory, granulomatous vasculitis. The expression of CCR5 on NK cells was up-regulated in individuals with HIV viremia and in individuals with active WG, indicating that expression of this receptor is modulated by states of immune activation associated with viral infection and inflammatory or immune-mediated diseases. In contrast, iNKRs were shown to be up-regulated only on NK cells of individuals with HIV viremia, and they returned to a normal level when viremia was controlled with effective antiviral therapy. In individuals with HIV-1 viremia, there was a direct correlation between the level of expression of p58.1, p58.2, and CD94 receptors and plasma HIV viremia, suggesting that ongoing active HIV replication has an effect on the expression of such receptors on NK cells. These results suggest that immune activation leads to abnormal cell-surface expression of chemokine receptors on NK cells, whereas HIV-specific processes account for the up-regulation of iNKRs on NK cells; this may explain the NK cell-functional defects seen in HIV infection.

Short-cycle structured intermittent treatment of chronic HIV infection with highly active antiretroviral therapy: effects on virologic, immunologic, and toxicity parameters

Although continuous highly active antiretroviral therapy (HAART) is effective for many HIV-infected patients, it can be toxic and prohibitive in cost. By decreasing the total amount of time patients receive medications, intermittent HAART could reduce toxicity and cost. Therefore, we initiated a pilot study in which 10 HIV-infected individuals receiving effective therapy that resulted in levels of HIV RNA <50 copies per ml of plasma and CD4(+) T cell counts >300 cells per mm(3) of whole blood received repeated cycles of 7 days on HAART followed by 7 days off of HAART. Patients maintained suppression of plasma viremia for 32-68 weeks. There was no significant increase in HIV proviral DNA or replication-competent HIV in peripheral CD4(+) T cells or HIV RNA in peripheral blood or lymph node mononuclear cells. There was no significant change in CD4(+) T cell counts, no significant increase in CD4(+) or CD8(+) T cells expressing activation markers or producing IFN-gamma in response to HIV, no increase in CD4(+) T cell proliferation to p24 antigen, and no evidence for the development of resistance to HAART medications. There was a significant decrease in serum cholesterol and triglyceride levels. Thus, in this proof-of-concept study, short-cycle intermittent HAART maintained suppression of plasma viremia as well as HIV replication in reservoir sites while preserving CD4(+) T cell counts. In addition, there was a decrease in serum cholesterol and triglyceride levels. Intermittent therapy may be an important strategy to reduce cost and toxicity for HIV-infected individuals.

Human immunodeficiency virus type 1 (HIV-1) non-B subtypes are similar to HIV-1 subtype B in that coreceptor specificity is a determinant of cytopathicity in human lymphoid tissue infected ex vivo

We sought to determine the relationship between virus-mediated CD4(+) T-lymphocyte cytopathicity and viral coreceptor preference among various human immunodeficiency virus type 1 (HIV-1) subtypes in an ex vivo-infected human lymphoid tissue model. Our data show that all R5 HIV-1 infections resulted in mild depletion of CD4(+) T lymphocytes, whereas all X4 HIV-1 infections caused severe depletion of CD4(+) T lymphocytes regardless of their subtype origin. Thus, at least for the viruses within subtypes A, B, C, and E that were tested, coreceptor specificity is a critical factor that determines the ability of HIV-1 to deplete CD4(+) T cells in human lymphoid tissue infected ex vivo.

Protection of rhesus macaques against disease progression from pathogenic SHIV-89.6PD by vaccination with phage-displayed HIV-1 epitopes

The antigenic polymorphism of HIV-1 is a major obstacle in developing an effective vaccine. Accordingly, we screened random peptide libraries (RPLs) displayed on phage with antibodies from HIV-infected individuals and identified an array of HIV-specific epitopes that behave as antigenic mimics of conformational epitopes of gp120 and gp41 proteins. We report that the selected epitopes are shared by a collection of HIV-1 isolates of clades A-F. The phage-borne epitopes are immunogenic in rhesus macaques, where they elicit envelope-specific antibody responses. Upon intravenous challenge with 60 MID50 of pathogenic SHIV-89.6PD, all monkeys became infected; however, in contrast to the naive and mock-immunized monkeys, four of five mimotope-immunized monkeys experienced lower levels of peak viremia, followed by viral set points of undetectable or transient levels of viremia and a mild decline of CD4+ T cells, and were protected from progression to AIDS-like illness. These results provide a new approach to the design of broadly protective HIV-1 vaccines.

Research sheds light on treatment interruption

Although there still is no clear answer about using structured treatment interruption as a therapeutic method with HIV patients, the strategy is gaining more respect as researchers from around the world continue to study it. Intermittent therapy, in which patients stop their antiretroviral therapy and then resume therapy in a cyclic way, may prove feasible, says one expert who spoke about interrupted treatment at the First International AIDS Society Conference on HIV Pathogenesis and Treatment in Buenos Aires, Argentina.

HIV-1 induces phenotypic and functional perturbations of B cells in chronically infected individuals

A number of perturbations of B cells has been described in the setting of HIV infection; however, most remain poorly understood. To directly address the effect of HIV replication on B cell function, we investigated the capacity of B cells isolated from HIV-infected patients to respond to a variety of stimuli before and after reduction of viremia by effective antiretroviral therapy. B cells taken from patients with high levels of plasma viremia were defective in their proliferative responses to various stimuli. Viremia was also associated with the appearance of a subpopulation of B cells that expressed reduced levels of CD21. After fractionation into CD21(high)- and CD21(low)-expressing B cells, the CD21(low) fraction showed dramatically reduced proliferation in response to B cell stimuli and enhanced secretion of immunoglobulins when compared with the CD21(high) fraction. Electron microscopic analysis of each fraction revealed cells with plasmacytoid features in the CD21(low) B cell population but not in the CD21(high) fraction. These results indicate that HIV viremia induces the appearance of a subset of B cells whose function is impaired and which may be responsible for the hypergammaglobulinemia associated with HIV disease.

Treatment of primary human immunodeficiency virus type 1 infection with potent antiretroviral therapy reduces frequency of rapid progression to AIDS

Immunologic data supporting immediate antiretroviral therapy in primary human immunodeficiency virus type 1 (HIV-1) infection are emerging; however, clinical benefit has not been demonstrated. The clinical and virologic course of 47 patients who were enrolled from September 1993 through June 1996 and who were not initially treated with potent therapy was compared with the course of 20 patients who immediately began therapy with zidovudine, lamivudine, and indinavir. Demographic and baseline laboratory data were comparable. During 78 weeks of follow-up, the early-treatment cohort showed a reduced frequency of opportunistic infections (5% vs. 21.3%; relative risk, 0.11; P=.02), less frequent progression to AIDS (13% vs. 0%), and significantly less frequent nonopportunistic mucocutaneous disorders and respiratory infections (P<.01). Plasma HIV-1 RNA levels were <50 copies/mL in all patients who continued therapy; however, after 9--12 months, HIV-1 remained detectable in latently infected CD4(+) T cells and in lymph node mononuclear cells. Combination antiretroviral therapy during primary HIV-1 infection demonstrated a decreased frequency of minor opportunistic infections, mucocutaneous disorders, and respiratory infections and reduced progression to AIDS.

Infectious diseases: considerations for the 21st century

The discipline of infectious diseases will assume added prominence in the 21st century in both developed and developing nations. To an unprecedented extent, issues related to infectious diseases in the context of global health are on the agendas of world leaders, health policymakers, and philanthropies. This attention has focused both on scientific challenges such as vaccine development and on the deleterious effects of infectious diseases on economic development and political stability. Interest in global health has led to increasing levels of financial support, which, combined with recent technological advances, provide extraordinary opportunities for infectious disease research in the 21st century. The sequencing of human and microbial genomes and advances in functional genomics will underpin significant progress in many areas, including understanding human predisposition and susceptibility to disease, microbial pathogenesis, and the development new diagnostics, vaccines, and therapies. Increasingly, infectious disease research will be linked to the development of the medical infrastructure and training needed in developing countries to translate scientific advances into operational reality.

Suppression of HIV replication in the resting CD4+ T cell reservoir by autologous CD8+ T cells: implications for the development of therapeutic strategies

CD8+ T cell-mediated antiviral activity against HIV has been described consistently in infected individuals; however, the role of this activity in controlling replication of HIV in the latently infected, resting CD4+ T cell reservoir is unclear. By using an ex vivo system, we show that replication of HIV in this viral reservoir is effectively suppressed in coculture by autologous CD8+ T cells in long-term nonprogressors (LTNPs) and in patients whose viremia was controlled by highly active antiretroviral therapy (HAART), but not in therapy-naive patients who had substantial levels of plasma viremia. This antiviral activity was largely independent of cytotoxic CD8+ T lymphocytes (CTL). When the role of soluble CD8+ T cell-derived factors was examined, we found that CC-chemokines played a major role in inhibition of viral replication in the latent viral reservoir in some LTNPs and patients receiving HAART, but not in chronically infected patients who were not receiving antiretroviral therapy. Potent antiviral activity, independent of CC-chemokines, was found mainly in patients in whom HAART was initiated shortly after the acute phase of HIV infection. These results indicate that CD8(+) T cells provide potent suppressive activity against HIV replication in the latent viral reservoir via direct cellular contact in patients who are naturally LTNPs or in those who are treated with HAART. Furthermore, the profound antiviral activity exerted by non-CC-chemokine soluble factors in infected patients who began HAART early in HIV infection suggests that preservation of this HIV-suppressive mechanism by early initiation of therapy may play an important role in the containment of viral replication in infected patients following interruption of therapy.

The role of CD4+ T cell help and CD40 ligand in the in vitro expansion of HIV-1-specific memory cytotoxic CD8+ T cell responses

CD4(+) T cells have been shown to play a critical role in the maintenance of an effective anti-viral CD8(+) CTL response in murine models. Recent studies have demonstrated that CD4(+) T cells provide help to CTLs through ligation of the CD40 receptor on dendritic cells. The role of CD4(+) T cell help in the expansion of virus-specific CD8(+) memory T cell responses was examined in normal volunteers recently vaccinated to influenza and in HIV-1 infected individuals. In recently vaccinated normal volunteers, CD4(+) T cell help was required for optimal in vitro expansion of influenza-specific CTL responses. Also, CD40 ligand trimer (CD40LT) enhanced CTL responses and was able to completely substitute for CD4(+) T cell help in PBMCs from normal volunteers. In HIV-1 infection, CD4(+) T cell help was required for optimal expansion of HIV-1-specific memory CTL in vitro in 9 of 10 patients. CD40LT could enhance CTL in the absence of CD4(+) T cell help in the majority of patients; however, the degree of enhancement of CTL responses was variable such that, in some patients, CD40LT could not completely substitute for CD4(+) T cell help. In those HIV-1-infected patients who demonstrated poor responses to CD40LT, a dysfunction in circulating CD8(+) memory T cells was demonstrated, which was reversed by the addition of cytokines including IL-2. Finally, it was demonstrated that IL-15 produced by CD40LT-stimulated dendritic cells may be an additional mechanism by which CD40LT induces the expansion of memory CTL in CD4(+) T cell-depleted conditions, where IL-2 is lacking.

Filarial infections increase susceptibility to human immunodeficiency virus infection in peripheral blood mononuclear cells in vitro

Because helminth infections and human immunodeficiency virus (HIV) coexist in areas where the spread of AIDS is most dramatic, their in vitro interaction was explored. Cryopreserved peripheral blood mononuclear cells (PBMC) from patients with filarial infections (n=24) and from unexposed control subjects (n=12) were depleted of CD8 T cells and were infected with macrophage (M)- and T cell-tropic viruses. A trend toward increased HIV replication in PBMC from filaria-infected patients was observed. Furthermore, PBMC from 6 filaria-infected patients before antifilarial treatment were significantly more susceptible to replication of M-tropic virus than their posttreatment PBMC (P=.03). No intergroup differences were found in the surface expression of HLA-DR, CD25, CCR5, CXCR4, CCR3 on CD4 T cells, or monocytes before infection. PBMC from filaria-infected patients produced less RANTES (P=.02) but more intracellular interleukin-4 than those of control subjects. Thus, PBMC from persons with filarial infections appear to have enhanced susceptibility to HIV-1 infection mediated by an undetermined mechanism.

Chemokines, cytokines and HIV: a complex network of interactions that influence HIV pathogenesis

The important role of chemokine receptors in HIV pathogenesis is becoming increasingly apparent. The level at which certain chemokine receptors that serve as HIV co-receptors are available influences the susceptibility of a CD4+ cell to viral infection and to certain HIV envelope-induced alterations in cellular function. Numerous pathogens, including HIV, can stimulate the production of chemokines and cytokines from a variety of cell types. Both cytokines and chemokines modulate CCR5 and CXCR4 availability, resulting in differential replication potentials for RS and X4 HIV strains depending on the milieu in the microenvironment. In addition, differential expression of CCR5 and CXCR4 on activated memory T cells appears to play an important role in preferential replication of RS HIV strains in vivo. However, expression of HIV co-receptors and CD4 may not be sufficient for effective HIV entry and replication. Intracellular signaling events, triggered by interaction between chemokine receptors and chemokines or HIV envelope, are important for efficient entry and completion of early replication events. Envelope proteins of different HIV isolates vary in their ability to transduce these signals, a characteristic that may play a role in determining the ability of a virus to productively infect certain cell types. Finally, the interaction between chemokine receptors and chemokines or HIV envelope has significant effects on cellular functions which likely play a role in HIV pathogenesis.

B cells of HIV-1-infected patients bind virions through CD21-complement interactions and transmit infectious virus to activated T cells

The impact of HIV-associated immunopathogenesis on B cells has been largely associated with indirect consequences of viral replication. This study demonstrates that HIV interacts directly with B cells in both lymphoid tissues and peripheral blood. B cells isolated from lymph node and peripheral blood mononuclear cells (PBMCs) of 4 and 23 chronically infected patients, respectively, demonstrated similar capacities to pass virus to activated HIV-negative PBMCs when compared with CD4(+) cells from the same patients. However, in contrast to T cells, virus associated with B cells was surface bound, as shown by its sensitivity to pronase and the staining pattern revealed by in situ amplification of HIV-1 RNA. Cell sorting and ligand displacing approaches established that CD21 was the HIV-binding receptor on B cells, and that this association was mediated through complement-opsonized virus. These B cells were also found to express significantly lower levels of CD21 compared with HIV-negative individuals, suggesting a direct perturbing effect of HIV on B cells. These findings suggest that B cells, although they themselves are not readily infected by HIV, are similar to follicular dendritic cells in their capacity to serve as extracellular reservoirs for HIV-1. Furthermore, B cells possess the added capability of circulating in peripheral blood and migrating through tissues where they can potentially interact with and pass virus to T cells.

Cathepsin G, a neutrophil-derived serine protease, increases susceptibility of macrophages to acute human immunodeficiency virus type 1 infection

Neutrophils dominate acute inflammatory responses that generally evolve into chronic inflammatory reactions mediated by monocyte/macrophages and lymphocytes. The latter cell types also serve as major targets for human immunodeficiency virus type 1 (HIV-1). In this study we have investigated the role of neutrophil products, particularly cathepsin G, in HIV infection. Cathepsin G induced chemotaxis and production of proinflammatory cytokines by macrophages but not CD4(+) T cells. Pretreatment with cathepsin G markedly increased susceptibility of macrophages but not CD4(+) T cells to acute HIV-1 infection. When macrophages were exposed to pertussis toxin prior to cathepsin G treatment, the cathepsin G-mediated effect was almost abrogated, suggesting that enhancement of HIV-1 replication by cathepsin G requires Gi protein-mediated signal transduction. Although prolonged exposure to cathepsin G suppressed HIV infection of macrophages, serine protease inhibitors, which are exuded from the bloodstream later during inflammatory processes, neutralized the inhibitory effect. Neutrophil extracts or supernatants from neutrophil cultures, which contain cathepsin G, had effects similar to purified cathepsin G. Thus, cathepsin G, and possibly other neutrophil-derived serine proteases, may have multiple activities in HIV-1 infection of macrophages, including chemoattraction of monocyte/macrophages (HIV-1 targets) to inflamed tissue, activation of target cells, and increase in their susceptibility to acute HIV-1 infection.

CD40 ligand trimer and IL-12 enhance peripheral blood mononuclear cells and CD4+ T cell proliferation and production of IFN-gamma in response to p24 antigen in HIV-infected individuals: potential contribution of anergy to HIV-specific unresponsiveness

It has been suggested that CD4+ T cell proliferative responses to HIV p24 Ag may be important in the control of HIV infection. However, these responses are minimal or absent in many HIV-infected individuals. Furthermore, while in vitro and in vivo responses to non-HIV recall Ags improve upon administration of highly active antiretroviral therapy, there does not appear to be a commensurate enhancement of HIV-specific immune responses. It is possible that CD4+ p24-specific T cells are deleted early in the course of infection. However, it is also possible that a discrete unresponsiveness, or anergy, contributes to the lack of proliferation to p24. To evaluate the possible contribution of unresponsiveness to the lack of CD4+ T cell proliferation to p24 in HIV-infected individuals, we attempted to overcome unresponsiveness. CD40 ligand trimer (CD40LT) and IL-12 significantly increased PBMC and CD4+ T cell proliferative responses to p24 Ag in HIV-infected, but not uninfected, individuals. No increase in proliferative response to CMV Ag was observed. CD40LT exerted its effect through B7-CD28-dependent and IL-12- and IL-15-independent mechanisms. Finally, the increase in proliferation with CD40LT and IL-12 was associated with an augmented production of IFN-gamma in most, but not all, individuals. These data suggest the possible contribution of HIV-specific unresponsiveness to the lack of CD4+ T cell proliferation to p24 Ag in HIV-infected individuals and that clonal deletion alone does not explain this phenomenon. They also indicate the potential for CD40LT and IL-12 as immune-based therapies for HIV infection.

CCR5 signal transduction in macrophages by human immunodeficiency virus and simian immunodeficiency virus envelopes

The capacity of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) envelopes to transduce signals through chemokine coreceptors on macrophages was examined by measuring the ability of recombinant envelope proteins to mobilize intracellular calcium stores. Both HIV and SIV envelopes mobilized calcium via interactions with CCR5. The kinetics of these responses were similar to those observed when macrophages were treated with MIP-1beta. Distinct differences in the capacity of envelopes to mediate calcium mobilization were observed. Envelopes derived from viruses capable of replicating in macrophages mobilized relatively high levels of calcium, while envelopes derived from viruses incapable of replicating in macrophages mobilized relatively low levels of calcium. The failure to efficiently mobilize calcium was not restricted to envelopes derived from CXCR4-utilizing isolates but also included envelopes derived from CCR5-utilizing isolates that fail to replicate in macrophages. We characterized one CCR5-utilizing isolate, 92MW959, which entered macrophages but failed to replicate. A recombinant envelope derived from this virus mobilized low levels of calcium. When macrophages were inoculated with 92MW959 in the presence of MIP-1alpha, viral replication was observed, indicating that a CC chemokine-mediated signal provided the necessary stimulus to allow the virus to complete its replication cycle. Although the role that envelope-CCR5 signal transduction plays in viral replication is not yet understood, it has been suggested that envelope-mediated signals facilitate early postfusion events in viral replication. The data presented here are consistent with this hypothesis and suggest that the differential capacity of viral envelopes to signal through CCR5 may influence their ability to replicate in macrophages.

Relationship between pre-existing viral reservoirs and the re-emergence of plasma viremia after discontinuation of highly active anti-retroviral therapy

We examined the pathogenic significance of the latent viral reservoir in the resting CD4+ T cell compartment of HIV-1-infected individuals as well as its involvement in the rebound of plasma viremia after discontinuation of highly active anti-retroviral therapy (HAART). Using heteroduplex mobility and tracking assays, we show that the detectable pool of latently infected, resting CD4+ T cells does not account entirely for the early rebounding plasma HIV in infected individuals in whom HAART has been discontinued. In the majority of patients examined, the rebounding plasma virus was genetically distinct from both the cell-associated HIV RNA and the replication-competent virus within the detectable pool of latently infected, resting CD4 + T cells. These results indicate the existence of other persistent HIV reservoirs that could prompt rapid emergence of plasma viremia after cessation of HAART and underscore the necessity to develop therapies directed toward such populations of infected cells.

In vitro reactivation of human immunodeficiency virus 1 from latently infected, resting CD4+ T cells after bacterial stimulation

Microbial coinfections have been associated with transient bursts of human immunodeficiency virus (HIV) viremia in patients. In this study, we have investigated whether microbial coinfections can induce replication of HIV-1 in latently infected CD4(+) T cells derived from HIV-infected patients who are receiving highly active antiretroviral therapy and in whom plasma viremia is undetectable by sensitive assays. We demonstrate that supernatants from macrophages exposed to the bacterial product lipopolysaccharide can induce in vitro activation of HIV-1 from latently infected, resting CD4(+) T cells obtained from HIV-infected individuals. Depletion of proinflammatory cytokines from the supernatant markedly reduced-whereas depletion of ss chemokines increased--the ability of the supernatant to induce replication of HIV-1. Our results suggest that coinfection with microbial pathogens such as bacteria may induce viral replication in the latent viral reservoirs in vivo.

Evaluation of lymph node virus burden in human immunodeficiency virus-infected patients receiving efavirenz-based protease inhibitor--sparing highly active antiretroviral therapy

Although efavirenz-containing regimens effectively suppress plasma levels of human immunodeficiency virus (HIV) RNA, it is now clear that undetectable plasma viremia may not reflect a lack of viral replication. Because lymphoid tissue is an active site of HIV replication, the lymph node virus burden was analyzed in persons who received highly active antiretroviral therapy (HAART) containing either efavirenz or a protease inhibitor (PI). Testing with in situ hybridization revealed no detectable follicular dendritic cell-associated HIV RNA in either group, and only 2 of 8 persons in the efavirenz group and 1 of 4 in the PI group had detectable RNA in lymph node mononuclear cells (LNMC) when tested by use of nucleic acid sequencebased amplification. Low levels of replication-competent HIV were identified in both groups by use of quantitative coculture assays. There was no evidence of development of resistance to either regimen in virus isolated from LNMC. These data support the use of efavirenz as an alternative to a PI in initial HAART regimens.

HIV-1 envelope induces activation of caspase-3 and cleavage of focal adhesion kinase in primary human CD4(+) T cells

Binding of HIV type 1 (HIV-1) envelope glycoproteins to the surface of a CD4(+) T cell transduces intracellular signals through the primary envelope receptor, CD4, and a coreceptor, either CCR5 or CXCR4. Furthermore, envelope-CD4(+) cell interactions increase rates of apoptosis in peripheral blood mononuclear cells (PBMCs). We demonstrate that in primary T lymphocytes, recombinant HIV-1 envelope proteins induce the activation of caspase-3 and caspase-6, which belong to a family of cysteine proteases that, upon activation, promote programmed cell death. Envelope-mediated activation of caspase-3 and caspase-6 depended on envelope-CD4 receptor interactions; CCR5-utilizing as well as CXCR4-utilizing envelopes elicited this response. Focal adhesion kinase (FAK) is a substrate of both caspase-3 and caspase-6, and inactivation of FAK by these caspases promotes apoptosis. En-velope treatment of lymphocytes led to the cleavage of FAK in a manner consistent with caspase-mediated cleavage.

HIV-1 and T cell dynamics after interruption of highly active antiretroviral therapy (HAART) in patients with a history of sustained viral suppression

Identifying the immunologic and virologic consequences of discontinuing antiretroviral therapy in HIV-infected patients is of major importance in developing long-term treatment strategies for patients with HIV-1 infection. We designed a trial to characterize these parameters after interruption of highly active antiretroviral therapy (HAART) in patients who had maintained prolonged viral suppression on antiretroviral drugs. Eighteen patients with CD4(+) T cell counts >/= 350 cells/microliter and viral load below the limits of detection for >/=1 year while on HAART were enrolled prospectively in a trial in which HAART was discontinued. Twelve of these patients had received prior IL-2 therapy and had low frequencies of resting, latently infected CD4 cells. Viral load relapse to >50 copies/ml occurred in all 18 patients independent of prior IL-2 treatment, beginning most commonly during weeks 2-3 after cessation of HAART. The mean relapse rate constant was 0.45 (0.20 log(10) copies) day(-1), which was very similar to the mean viral clearance rate constant after drug resumption of 0.35 (0.15 log(10) copies) day(-1) (P = 0.28). One patient experienced a relapse delay to week 7. All patients except one experienced a relapse burden to >5,000 RNA copies/ml. Ex vivo labeling with BrdUrd showed that CD4 and CD8 cell turnover increased after withdrawal of HAART and correlated with viral load whereas lymphocyte turnover decreased after reinitiation of drug treatment. Virologic relapse occurs rapidly in patients who discontinue suppressive drug therapy, even in patients with a markedly diminished pool of resting, latently infected CD4(+) T cells.

Selective pressure exerted by immunodominant HIV-1-specific cytotoxic T lymphocyte responses during primary infection drives genetic variation restricted to the cognate epitope

HIV-specific cytotoxic T lymphocytes (CTL) play a central role in the control of HIV-1 replication during primary infection. It has been hypothesized that the appearance of CTL escape mutants represents an important mechanism by which HIV-1 escapes the host cell-mediated immune response. However, evidences for a direct relationship between CTL responses and emergence of CTL escape mutants are still limited. Here we report detailed longitudinal analysis of DNA sequence variation performed over the entire HIV-1 envelope in two subjects during primary HIV infection. Estimates of the frequencies of synonymous (ds) and non-synonymous (dN) nucleotide substitutions were used to identify regions of the HIV-1 envelope which were subjected to significant levels of selective pressure. These regions were shown to comprise defined epitopes recognized by CTL. Furthermore, dN mutation fixed within these epitopes effectively abolished recognition by the host CTL response. These results provide compelling evidence that the CTL epitope mutations directly resulted from the selective pressure exerted by the virus-specific cytotoxic response.

CD40-Mediated induction of CD4 and CXCR4 on B lymphocytes correlates with restricted susceptibility to human immunodeficiency virus type 1 infection: potential role of B lymphocytes as a viral reservoir

Human immunodeficiency virus type 1 (HIV-1) replicates primarily in lymphoid tissues where it has ready access to activated immune competent cells. We used one of the major pathways of immune activation, namely, CD40-CD40L interactions, to study the infectability of B lymphocytes isolated from peripheral blood mononuclear cells. Highly enriched populations of B lymphocytes generated in the presence of interleukin-4 and oligomeric soluble CD40L upregulated costimulatory and activation markers, as well as HIV-1 receptors CD4 and CXCR4, but not CCR5. By using single-round competent luciferase viruses complemented with either amphotropic or HIV-derived envelopes, we found a direct correlation between upregulation of HIV-1 receptors and the susceptibility of the B lymphocytes to infection with dual-tropic and T-tropic strains of HIV-1; in contrast, cells were resistant to M-tropic strains of HIV-1. HIV-1 envelope-mediated infection was completely abolished with either an anti-CD4 monoclonal antibody or a peptide known to directly block CXCR4 usage and partially blocked with stromal cell-derived factor 1, all of which had no effect on the entry of virus pseudotyped with amphotropic envelope. Full virus replication kinetics confirmed that infection depends on CXCR4 usage. Furthermore, productive cycles of virus replication occurred rapidly yet under most conditions, without the appearance of syncytia. Thus, an activated immunological environment may induce the expression of HIV-1 receptors on B lymphocytes, priming them for infection with selective strains of HIV-1 and allowing them to serve as a potential viral reservoir.

Latent reservoirs of HIV: obstacles to the eradication of virus

The use of highly active antiretroviral therapy (HAART) in the treatment of HIV-1-infected individuals has provided a considerable amount of information regarding the dynamics of viral replication and has resulted in enormous advances in HIV therapeutics. The profound suppression of plasma viremia in HIV-infected individuals receiving HAART has resulted in a highly beneficial clinical effect and a dramatic decrease in the death rate attributable to AIDS. Nonetheless, the persistance of reservoirs of HIV, including latently infected, resting CD4+ T cells that can give rise to infectious HIV upon stimulation in vitro, has posed a sobering challenge to the long-term control or eradication of HIV in infected individuals receiving HAART. Although a recent study has demonstrated th at the size of the pool of latently infected, resting CD4+ T cells can be markedly diminished with intermittent interleukin (IL-2) and continuous HAART, complete eradication of HiV in infected individuals remains extremely problematic. Here we discuss recent developments in studies of the latent reservoir of HIV in patients receiving HAART and implications for the long-term treatment of infected individuals and eradication of the infection.

Both memory and CD45RA+/CD62L+ naive CD4(+) T cells are infected in human immunodeficiency virus type 1-infected individuals

Cellular activation is critical for the propagation of human immunodeficiency virus type 1 (HIV-1) infection. It has been suggested that truly naive CD4(+) T cells are resistant to productive HIV-1 infection because of their constitutive resting state. Memory and naive CD4(+) T-cell subsets from 11 HIV-1-infected individuals were isolated ex vivo by a combination of magnetic bead depletion and fluorescence-activated cell sorting techniques with stringent criteria of combined expression of CD45RA and CD62L to identify naive CD4(+) T-cell subsets. In all patients HIV-1 provirus could be detected within naive CD45RA+/CD62L+ CD4(+) T cells; in addition, replication-competent HIV-1 was isolated from these cells upon CD4(+) T-cell stimulation in tissue cultures. Memory CD4(+) T cells had a median of fourfold more replication-competent virus and a median of sixfold more provirus than naive CD4(+) T cells. Overall, there was a median of 16-fold more integrated provirus identified in memory CD4(+) T cells than in naive CD4(+) T cells within a given patient. Interestingly, there was a trend toward equalization of viral loads in memory and naive CD4(+) T-cell subsets in those patients who harbored CXCR4-using (syncytium-inducing) viruses. Within any given patient, there was no selective usage of a particular coreceptor by virus isolated from memory versus naive CD4(+) T cells. Our findings suggest that naive CD4(+) T cells may be a significant viral reservoir for HIV, particularly in those patients harboring CXCR4-using viruses.

Induction of phosphorylation and intracellular association of CC chemokine receptor 5 and focal adhesion kinase in primary human CD4+ T cells by macrophage-tropic HIV envelope

Binding of HIV-1 envelope glycoproteins to the surface of a CD4+ cell transduces intracellular signals through the primary envelope receptor, CD4, and/or the envelope coreceptor, a seven-transmembrane chemokine receptor. Macrophage-tropic strains of HIV-1 preferentially use CCR5 as an entry coreceptor, whereas T cell-tropic strains use CXC chemokine receptor-4 for entry. Intracellular signals transduced by HIV-1 envelope may have immunopathogenic consequences, including anergy, syncytium formation, apoptosis, and inappropriate cell trafficking. We demonstrate here that a recombinant envelope protein derived from an M-tropic isolate of HIV-1 can transduce CD4-dependent as well as CCR5-dependent intracellular signals in primary human CD4+ T cells. Novel HIV-induced intracellular signals that were identified include tyrosine phosphorylation of focal adhesion kinase (FAK) and CCR5, which are involved in cell adhesion and chemotaxis, respectively. HIV envelope-induced cellular association of FAK and CCR5 was also demonstrated, suggesting that ligation of CD4 and CCR5 leads to the formation of an activation complex composed of FAK and CCR5. Activation of this signaling pathway by HIV-1 envelope may be an important pathogenic mechanism of dysregulated cellular activation and trafficking during HIV infection.

Induction of HIV-1 replication by allogeneic stimulation

Allogeneic stimulation presents an immunologic challenge during pregnancy, blood transfusions, and transplantations, and has been associated with reactivation of latently infected virus such as CMV. Since HIV-1 is transmitted vertically, sexually, or via contaminated blood, we have tested the effects of allostimulation on HIV-1 infection. 1) We show that allostimulated lymphocytes are highly susceptible to acute infection with T cell-tropic or dual-tropic HIV-1. 2) We show that allostimulation has dichotomous effects on replication of macrophage-tropic HIV-1; it activates HIV expression in already infected cells but inhibits HIV entry by secreting HIV-suppressive CC chemokines. 3) We show that allogeneic stimulation of latently infected, resting CD4+ T cells induced replication of HIV-1 in these cells. These observations suggest that allogeneic stimulation may play a role in the transmission, replication, and phenotypic transition of HIV-1.

HTLV type I Tax activation of the CXCR4 promoter by association with nuclear respiratory factor 1

Human T lymphotropic virus type I trans-activator Tax protein regulates expression of several cellular genes that are involved in cellular activation, proliferation, and transformation. Tax mediates its regulatory activity through interaction with cellular transcription factors such as members of the cAMP-responsive element-binding factors/ATF family or the NF-kappaB/Rel family. In this study we have demonstrated that Tax trans-activates the promoter for CXCR4, a coreceptor for T cell-tropic HIV-1 through its association with nuclear respiratory factor 1 (NRF1). The promoter region for CXCR4 contains an NRF1-binding site, which is crucial for basal and Tax-induced activity. Glutathione S-transferase (GST) pull-down experiments showed association of GST-Tax fusion protein with NRF1 in vitro. Expression of Tax, in addition to stimulation with phorbol myristate acetate and ionomycin, increased formation of the NRF1 complex in a gel-mobility shift assay, indicating that Tax association with NRF1 in vivo facilitates its DNA binding. HTLV-I Tax activation of CXCR4 may contribute to the rapid progression of HIV disease observed in certain coinfected individuals.

Effect of interleukin-2 on the pool of latently infected, resting CD4+ T cells in HIV-1-infected patients receiving highly active anti-retroviral therapy

The size of the pool of resting CD4+ T cells containing replication-competent HIV in the blood of patients receiving intermittent interleukin (IL)-2 plus highly active anti-retroviral therapy (HAART) was significantly lower than that of patients receiving HAART alone. Virus could not be isolated from the peripheral blood CD4+ T cells in three patients receiving IL-2 plus HAART, despite the fact that large numbers of resting CD4+ T cells were cultured. Lymph node biopsies were done in two of these three patients and virus could not be isolated. These results indicate that the intermittent administration of IL-2 with continuous HAART may lead to a substantial reduction in the pool of resting CD4+ T cells that contain replication-competent HIV.

USF/c-Myc enhances, while Yin-Yang 1 suppresses, the promoter activity of CXCR4, a coreceptor for HIV-1 entry

Transcription factors USF1 and USF2 up-regulate gene expression (i.e. , HIV-1 long terminal repeats) via interaction with an E box on their target promoters, which is also a binding site for c-Myc. The c-Myc oncoprotein is important in control of cellular proliferation and differentiation, while Yin-Yang 1 (YY1) has been shown to control the expression of a number of cellular and viral genes. These two proteins physically interact with each other and mutually inhibit their respective biological functions. In this study, we show that USF/c-Myc up-regulates, while YY1 down-regulates the promoter activity of CXCR4, a coreceptor for T cell-tropic HIV-1 entry. We have identified an E box around -260 and a YY1 binding site around -300 relative to the transcription start site. Mutation of the E box abolished USF/c-Myc-mediated up-regulation of CXCR4 promoter activity, and mutation of the YY1 binding site was associated with unresponsiveness to YY1-mediated inhibition. These data suggest that USF/c-Myc and YY1 may play an important role in the HIV-1-replicative cycle, by modulating both the viral fusion/entry process and viral expression.

Selection of HIV-specific immunogenic epitopes by screening random peptide libraries with HIV-1-positive sera

Efforts to develop a protective HIV-1 vaccine have been hindered by difficulties in identifying epitopes capable of inducing broad neutralizing Ab responses. In fact, the high mutation rate occurring in HIV-1 envelope proteins and the complex structure of gp120 as an oligomer associated with gp41 result in a high degree of antigenic polymorphism. To overcome these obstacles, we screened random peptide libraries using sera from HIV-infected subjects to identify antigenic and immunogenic mimics of HIV-1 epitopes. After extensive counterscreening with HIV-negative sera, we isolated peptides specifically recognized by Abs from HIV-1-infected individuals. These peptides behaved as antigenic mimics of linear or conformational HIV-1 epitopes generated in vivo in infected subjects. Consistent with these findings, sera of simian HIV-infected monkeys also recognized the HIV-specific epitopes. The selected peptides were immunogenic in mice, where they elicited HIV-specific Abs that effectively neutralized HIV-1 isolates. These results demonstrate that pools of HIV-1 mimotopes can be selected from combinatorial peptide libraries by taking advantage of the HIV-specific Ab repertoire induced by the natural infection.

Differential effects of CD40 ligand/trimer stimulation on the ability of dendritic cells to replicate and transmit HIV infection: evidence for CC-chemokine-dependent and -independent mechanisms

The role of exogenous stimulation of CD40 by CD40 ligand (CD40L) in dendritic cell (DC) maturation, CC-chemokine production, and CCR5 receptor expression was examined using a soluble trimeric CD40L agonist protein (CD40LT). Stimulation of monocyte-derived DCs with CD40LT enhanced the production of the CC-chemokines macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, and RANTES and diminished surface expression of CCR5. Based on these findings, the functional role of CD40LT stimulation on the ability of DCs to replicate and transmit HIV viral infection was studied. The addition of CD40LT to cocultures of naive CD4+ T cells and autologous DCs (T/DC) infected with the macrophage-tropic isolate, HIVBaL, caused a striking reduction in reverse transcriptase (RT) activity after 10 and 14 days of culture. The addition of a mixture of Abs against CC-chemokines abrogated the decrease in RT activity, demonstrating that the inhibitory effect mediated by CD40LT was CC-chemokine-dependent. In contrast, the presence of CD40LT in T/DC cocultures infected with the T cell-tropic isolate, HIV IIIB, caused an increase in RT activity that was CC-chemokine-independent. Of note, CD40LT stimulation also inhibited RT activity in cultures containing macrophage-tropic virus (HIVBaL)-infected DC only. However, in contrast to the results seen in the T/DC cocultures, CD40LT stimulation inhibited RT activity in cultures of DCs alone in a CC-chemokine-independent manner. Together, these results show that CD40LT stimulation of DCs suppresses HIV replication and transmission to CD4+ T cells by two potentially different mechanisms.